DISKOTIC MULTIYNE LANGMUIR-BLODGETT-FILMS .2. AGGREGATE AND MONOMER UV-VIS ABSORPTION AND FLUORESCENCE

Absorption and fluorescence spectra of a new multiyne diskotic compoun d is studied in thin films and solutions. A detailed energy diagram of the monomer absorption transitions is derived. A correlation between the structural organization of the diskotic Langmuir-Blodgett films, c haracterized in part 1, and their optical properties is found. The sig nificance of the pi-pi interactions in determining the type of the mol ecular aggregation is illustrated for the disk-shaped aromatic compoun ds considered in part 1. A set of rules are deduced on the basis of th e electrostatic theory of the pi-pi interactions to predict the prefer red type of diskotic liquid-crystalline phases depending on the molecu lar peculiarities and arrangement. The effect of the intra- and interl ayer molecular aggregation, environment and ct-electron interactions o n the optical properties of the diskotic films is discussed. The prefe rential orientations of the main transitional dipoles is determined us ing polarized absorption. The red shift of the J-aggregate bands evide nce the nematic arrangement of the disk-like molecules in the monolaye rs. Anomalous fluorescence with quantum yield of 0.36 is found.